Mobile construction equipment such as tractors outfitted with a hydraulically operated articulated work arm carrying any one of a variety of attachments are used for a wide variety of applications. In particular, they are critical machines in the construction of buildings, transportation channels, and almost any other man-made structure. A practical matter involves the transport of such equipment—such as, for example, a backhoe—between the physical locations where it will be used. If the equipment is driven to the desired location over roadways, difficulties associated with the weight distribution of the equipment often arise. In particular, the overhanging, leveraged weight of the backhoe linkage assembly increases the difficulty of controlling the equipment during transportation. The distribution of weight of the backhoe linkage assembly can affect equipment weight balance sufficiently that the weight remaining on the front wheels is lessened and steering control and ride comfort may be compromised.
A common approach to dealing with the undesirable weight distribution of this type of construction equipment is to add weight to the front of the machine to counter the weight of the backhoe linkage assembly. However, this solution is undesirable for several reasons. The additional weight causes the equipment to become more difficult to maneuver, especially in soft ground, more difficult to steer, and more clumsy to operate. In addition, fuel consumption is increased and the equipment cost effectiveness is decreased.
A more desirable solution to the problem of weight distribution has been to move the backhoe linkage assembly into a stored position where its weight is closer to the center of the equipment. For example, Case Corporation of Racine, Wis. builds backhoe-type machines with a distinctive feature, known as an “over-center” system, that permits the weight of the backhoe to be moved closer to the center of gravity of the equipment, whereby the weight moment arm is reduced. By shifting the weight of the backhoe toward the equipment's center of gravity, the need for a front-end counter-weight is eliminated. The “over-center” position of the backhoe linkage assembly is frequently known as the “carry,” the “latched,” or the “transport” position. The “over-center” system, as noted above, increases the maneuverability of the equipment, particularly in soft ground, and increases the stability of the equipment during road transportation.
While the “over-center” system provides significant benefits, use of the system requires operator skills that are acquired only through experience. Thus, while not always difficult for regular operators of the equipment, the technique may often be awkward for new or occasional operators of the machine. The technique involves a combination of operator actions that must be completed in timed sequence. The technique of moving the backhoe linkage assembly into the “over-center” position requires the operator to activate the lift cylinder and raise the work arm toward its uppermost position. At the moment that the lift cylinder is at its minimum length, the operator must then rapidly change the direction of the hydraulic control spool to reverse the direction of the lift cylinder operation, thereby driving the backhoe linkage assembly into the “over-center” transport position. If the directional change of its control spool is not effected at the correct moment, the backhoe assembly will fail to reach the transport position. The entire process must then be repeated. First-time operators and operators without significant experience often have difficulty performing the technique.
One solution is described in U.S. Pat. No. 6,267,548 which is directed to a control circuit for use in combination with an apparatus having a hydraulically operated articulated work arm, such as a backhoe machine, for which there are desired arm positions, such as an “over-center” transport position. The control circuit that is used in combination with the apparatus has a valve, preferably a solenoid valve; a source of electricity for operating the solenoid valve; and a switching mechanism. The solenoid valve is operably connected with the work arm hydraulic operating system. The control circuit provides an apparatus for reducing the importance of operator performance in placing equipment work arms into the over-center storage/transport position. Thus, new and less experienced operators can prepare the backhoe for travel between work sites.
While the prior art allows for a type of over-center boom assist, it would be beneficial to provide a further simplified boom-stowing process by making it possible to stow the boom more reliably at multiple boom speeds and with a less violent latching action.